Intestinal responses to Clostridium perfringens in broilers
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Date
02/07/2016Author
Russell, Katherine Margaret
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Abstract
Clostridium perfringens is the aetiological agent of Necrotic enteritis (NE); a
disease that impacts on the health and welfare of broilers. This disease is a
large cost to the industry and presents as lesions in the small intestine
hindering productivity. Antibiotics are commonly used to treat NE but as
pressure increases to limit their use further information about disease onset
and broiler responses to the bacteria and it’s virulence factors during
infection is required to implement new preventative measures and
treatments.
NetB is a secreted toxin from C. perfringens which has an important role in
NE onset. Using an in situ intestinal loop model we have been able to
characterise: I) temporal broiler responses to NetB positive bacterial culture
supernatant (Chapter 2), ii) early host responses to different isolates
possessing NetB (virulent) or not (avirulent) in the presence or absence of
bacterial cells (Chapter 3) and iii) the responses of two commercial broiler
breeds (Chapter 4) four hours post exposure. Samples collected from these
experiments have been used for histology, mRNA expression and
immunohistology.
We have shown differences in mRNA expression in the duodenum of broilers
after exposure to C. perfringens cells as well as the culture supernatant from
the isolates used after four hours. The presence of bacteria cells resulted in
up-regulation of pro-inflammatory cytokine, IFN-γ, mRNA, whereas it
resulted in down-regulation of B-LA, mRNA a gene involved in presentation
of pathogens to immune cells. IL-6 mRNA expression was also reduced in the
presence of virulent isolates. This could indicate a possible evasion strategy
for C. perfringens in broilers. Immunohistochemical analysis indicated that
slower growing broilers have increased numbers of immune cells
(macrophages and γδ T cells) in their duodenum compared with faster
growing broilers, although this did not appear to have an effect on mRNA
expression levels of pro-inflammatory cytokines, 4h post antigen infusion.
Overall we detect greater changes when bacteria are included with culture
supernatant and have highlighted possible mechanisms for C. perfringens to
avoid the broiler immune system.
Induction of NE in the literature requires pre-disposing factors, including co-infection
with other intestinal pathogens and dietary manipulation of the
host. The final experiment trialled protocols administering a virulent isolate
of C. perfringens in-feed and via gavage along with an increased protein
source to induce NE (Chapter 5). These models were not considered to be
consistent for further investigation of NE in the future.